A program has been established for the routine analyses of feed samples for chlorinated hydrocarbons, polychlorinated biphenyls, organo-phosphates, lead, arsenic, cadmium, mercury, nitrate and aflatoxins. Nitrosamine assays are being conducted on feed samples selected at random. The objective of this program is to document the concentrations of these potential contaminants in natural ingredient laboratory animal diets and to establish the maximal permissible concentrations that can be attained on a practical basis.